Summary of GDB commands for x86-64 Systems - Carnegie Mellon University

[Pages:2]Summary of GDB commands for x86-64 Systems

Command

Effect

Starting: gdb gdb

Running and stopping

quit

Exit gdb

run

Run program

run 1 2 3

Run program with command-line arguments 1 2 3

kill

Stop the program

quit

Exit gdb

Ctrl-d

Exit gdb

Note: Ctrl-C does not exit from gdb, but halts the current

gdb command

Breakpoints

break sum break *0x80483c3 delete 1 disable 1

enable 1 delete clear sum

Set breakpoint at the entry to function sum Set breakpoint at address 0x80483c3 Delete breakpoint 1 Disable the breakpoint 1

(gdb numbers each breakpoint you create) Enable breakpoint 1 Delete all breakpoints Clear any breakpoints at the entry to function sum

Execution

stepi stepi 4 nexti

step continue until 3 finish call sum(1, 2)

Execute one instruction Execute four instructions Like stepi, but proceed through function calls without stopping Execute one C statement Resume execution until the next breakpoint Continue executing until program hits breakpoint 3 Resume execution until current function returns Call sum(1,2) and print return value

Examining code

disas

Disassemble current function

disas sum

Disassemble function sum

disas 0x80483b7

Disassemble function around 0x80483b7

disas 0x80483b7 0x80483c7 Disassemble code within specified address range

print /x $rip print /d $rip print /t $rip

Print program counter in hex Print program counter in decimal Print program counter in binary

Examining data

print /d $rax print /x $rax print /t $rax print /d (int)$rax

Print contents of %rax in decimal Print contents of %rax in hex Print contents of %rax in binary Print contents of %rax in decimal after sign-extending lower 32-bits.

You need this to print 32-bit, negative numbers stored in the lower 32 bits of %rax. For example, if the lower 32-bits of %rax store 0xffffffff, you will see

(gdb) print $rax $1 = 4294967295 (gdb) print (int)$rax $2 = -1 (gdb)

print 0x100

Print decimal representation of 0x100

print /x 555

Print hex representation of 555

print /x ($rsp+8)

Print (contents of %rsp) + 8 in hex

print *(int *) 0xbffff890 Print integer at address 0xbffff890

print *(int *) ($rsp+8) Print integer at address %rsp + 8

print (char *) 0xbfff890 Examine a string stored at 0xbffff890

x/w 0xbffff890

x/w $rsp x/wd $rsp

x/2w $rsp

x/2wd $rsp

x/g $rsp x/gd $rsp

x/a $rsp

x/s 0xbffff890 x/20b sum x/10i sum

Examine (4-byte) word starting at address 0xbffff890 Examine (4-byte) word starting at address in $rsp Examine (4-byte) word starting at address in $rsp. Print in decimal Examine two (4-byte) words starting at address in $rsp Examine two (4-byte) words starting at address in $rsp. Print in decimal Examine (8-byte) word starting at address in $rsp. Examine (8-byte) word starting at address in $rsp. Print in decimal Examine address in $rsp. Print as offset from previous global symbol. Examine a string stored at 0xbffff890 Examine first 20 opcode bytes of function sum Examine first 10 instructions of function sum

(Note: the format string for the `x' command has the general form x/[NUM][SIZE][FORMAT] where

NUM = number of objects to display SIZE = size of each object (b=byte, h=half-word, w=word,

g=giant (quad-word)) FORMAT = how to display each object (d=decimal, x=hex, o=octal, etc.)

If you don't specify SIZE or FORMAT, either a default value, or the last value you specified in a previous `print' or `x' command is used. )

Useful information

backtrace where

Print the current address and stack backtrace Print the current address and stack backtrace

info program info functions info stack info frame info registers info breakpoints

Print current status of the program) Print functions in program Print backtrace of the stack) Print information about the current stack frame Print registers and their contents Print status of user-settable breakpoints

display /FMT EXPR

undisplay help

Print expression EXPR using format FMT every time GDB stops Turn off display mode Get information about gdb

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